The present invention is directed to novel gels and their uses.
Like (SEPS) poly(styrene-ethylene-propylene-styrene), random mixtures of ethylene and butylene midblock copolymer segment of conventional SEBS poly(styrene-ethylene-butylene-styrene) block copolymers is almost totally amorphous, substantially free of any crystallinity or non-crystalline. Such SEBS block copolymers with substantially non-crystalline ethylene-butylene elastomer midblock segment are used for making elastomeric gels of varying rigidities which can vary from soft to firm. Such gels are hereafter referred to as xe2x80x9cnon-crystalline midblock gelsxe2x80x9d or xe2x80x9camorphous midblock gelsxe2x80x9d or more simply xe2x80x9camorphous gelsxe2x80x9d. Generally, the properties of amorphous gels increase with increasing gel rigidity. The amorphous gels at any rigidity, however, can fail catastrophically when cut or notched while under applied forces of high dynamic and static deformations, such as extreme compression, torsion, high tension, high elongation, and the like. Additionally, the development of cracks or crazes resulting from a large number of deformation cycles can induce catastrophic fatigue failure of amorphous gel composites, such as tears and rips between the surfaces of the amorphous gel and substrates or at the interfaces of interlocking material(s) and amorphous gel. Consequently, such amorphous gels made from SEPS and SEBS are inadequate for the most demanding applications involving endurance at high stress and strain levels over an extended period of time.
I have now discovered novel gels with improved properties made from thermoplastic elastomer copolymers and block copolymers having one or more substantially crystalline polyethylene segment midblocks exhibiting greater advantage over other non-crystalline component forming gels. The crystal gels advantageously exhibit high, higher, and ever higher tear resistances than ever realized before as well as improved high tensile strength.
The advances in improved properties of the crystal gels over amorphous gels are many, these include: improved damage tolerance, improved crack propagation resistance, improved tear resistance, improved resistance to fatigue, etc. Such crystal gels are advantageous for end-use involving repeated applications of stress and strain resulting from large number of cycles of deformations, including compression, compression-extension (elongation), torsion, torsion-compression, torsion-elongation, tension, tension-compression, tension-torsion, etc. The crystal gels also exhibit improved damage tolerance, crack propagation resistance and especially improved resistance to high stress rupture which combination of properties makes the gels advantageously and surprisingly exceptionally more suitable than amorphous gels made from non-crystalline poly(ethylene) component copolymers at corresponding gel rigidities.
The crystal gels which are advantageously useful for making various toys, medical devices, and other useful articles of manufacture including disposable inflatable restraint cushions comprises: 100 parts by weight of one or more high viscosity (I) linear triblock copolymers, (II) multi-arm block copolymers, (III) branched block copolymers, (IV) radial block copolymers, (V) multiblock copolymers, (VI) random copolymers, (VII) thermoplastic crystalline polyurethane copolymers with hydrocarbon midblocks or mixtures of two or more (I)-(VII) copolymers in combination with or without major or minor amounts of one or more other (VIII) copolymers or polymers, said copolymers having one or more segments or one or more midblocks comprising one or more substantially crystalline polyethylene segments or midblocks and selected amounts of a compatible plasticizer (IX) sufficient to achieve gel rigidities of from less than about 2 gram Bloom to about 1,800 gram Bloom with the proviso that when said (I)-(VII) copolymers having nil amorphous segment or nil amorphous midblock are combined with one or more (VIII) copolymers having one or more amorphous segments or amorphous midblocks to form a stable plasticizer compatible gel.
As used herein, the term xe2x80x9cgel rigidityxe2x80x9d in gram Bloom is determined by the gram weight required to depress a gel a distance of 4 mm with a piston having a cross-sectional area of 1 square centimeter at 23xc2x0 C.
The gels comprising the thermoplastic elastomer copolymers and block copolymers having one or more substantially crystalline polyethylene segments or midblocks of the invention are hereafter referred to as xe2x80x9celastic-crystalline gelsxe2x80x9d or simpler xe2x80x9ccrystal gelsxe2x80x9d. The segments or midblocks of copolymers forming the crystal gels of the invention are characterized by sufficient crystallinity as to exhibit a melting endotherm of at least about 40xc2x0 C. as determined by DSC curve.
The various types of high viscosity copolymers and block copolymers employed in forming the crystal gels of the invention are of the general configurations (Y-AY)n copolymers, A-Z-A, and (A-Z)n block copolymers, wherein the subscript n is two, three, four, five or more. In the case of multiarm block copolymers where n is 2, the block copolymer denoted by (A-Z)n is A-Z-A. It is understood that the coupling agent is ignored for sake of simplicity in the description of the (A-Z)n block copolymers.
The segment (A) comprises a glassy amorphous polymer end block segment which can be polystyrene, poly(alpha-methylstyrene), poly(o-methylstyrene), poly(m-methylstyrene), poly(p-methylstyrene) and the like, preferably, polystyrene.
The segment (Y) of (VI) copolymers (Y-AY)n comprises substantially crystalline poly(ethylene) (simply denoted by xe2x80x9c-E-xe2x80x9d or (E)). In the case of (VI) copolymers (A-Y)n, (Y) when next to (A) may be substantially non-crystalline or amorphous ethylene segments. For example a crystalline copolymer (Y-AY)n may be represented by: . . . -E-E-E-E-E-E-E-E-E-SE-E-E-E-E-E-E-SE-E-E-E-E-E-E-SE- . . . Where Y is a long run of polyethylenes or a non-crystalline copolymer (AY-AY)n: . . . -E-SE-SE-E-SE-E-SE-E-SE-E-E-SE-SE-E-SE- . . . , Where Y is a non-crystalline run of ethylene.
The end block segment (A) comprises a glassy amorphous polymer end block segment which can be polystyrene, poly(alpha-methylstyrene), poly(o-methylstyrene), poly(m-methylstyrene), poly(p-methylstyrene) and the like, preferably, polystyrene. The segment (Y) of (VI) random copolymers A-Y comprises substantially crystalline poly(ethylene) (simply denoted by xe2x80x9c-E-xe2x80x9d or (E)). In the case of (VIII) random copolymers A-Y, (Y) may be substantially non-crystalline or amorphous ethylene segments. The midblocks (Z) comprises one or more midblocks of substantially crystalline poly(ethylene) (simply denoted by xe2x80x9c-E- or (E)xe2x80x9d) with or without one or more amorphous midblocks of poly(butylene), poly(ethylene-butylene), poly(ethylene-propylene) or combination thereof (the amorphous midblocks are denoted by xe2x80x9c-B- or (B)xe2x80x9d, xe2x80x9c-EB- or (EB)xe2x80x9d, and xe2x80x9c-EP- or (EP)xe2x80x9d respectively or simply denoted by xe2x80x9c-W- or (W)xe2x80x9d when referring to one or more of the amorphous midblocks as a group) The A and Z, and A and Y portions are incompatible and form a two or more-phase system consisting of sub-micron amorphous glassy domains (A) interconnected by (Z) or (Y) chains. The glassy domains serve to crosslink and reinforce the structure. This physical elastomeric network structure is reversible, and heating the polymer above the softening point of the glassy domains temporarily disrupt the structure, which can be restored by lowering the temperature. During mixing and heating in the presence of compatible plasticizers, the glassy domains (A) unlock due to both heating and solvation and the molecules are free to move when shear is applied. The disruption and ordering of the glassy domains can be viewed as a unlocking and locking of the elastomeric network structure. At equilibrium, the domain structure or morphology as a function of the (A) and (Z) or (A) and (Y) phases (mesophases) can take the form of spheres, cylinders, lamellae, or bicontinous structures. The scale of separation of the phases are typically of the order of hundreds of angstroms, depending upon molecular weights (i.e. Radii of gyration) of the minority-component segments. At such small domain scales, when the gel is in the molten state while heated and brought into contact to be formed with any substrate and allowed to cool, the glassy domains of the gel become interlocked with the surface the substrate. At sufficiently high enough temperatures, with or without the aid of other glassy resins, the glassy domains of the copolymers forming the gels fusses and interlocks with even a visibly smooth substrate surface such as glass. The disruption of the sub-micron domains due to heating above the softening point forces the glassy domains to open up, unlocking the network structure and flow. Upon cooling below the softing point, the glassy polymers reforms together into sub-micron domains, locking into a network structure once again, resisting flow. It is this unlocking and locking of the network structure on the sub-micron scale with the surfaces of various materials which allows the gel to form interlocking composites with other materials. Such interlocking with many different materials produce gel composites having many uses.
The (I) linear block copolymers are characterized as having a Brookfield Viscosity value at 5 weight percent solids solution in toluene at 30xc2x0 C. of from less than about 40 cps to about 60 cps and higher, advantageously from about 40 cps to about 160 cps and higher, more advantageously from about 50 cps to about 180 cps and higher, still more advantageously from about 70 cps to about 210 cps and higher, and even more advantageously from about 90 cps to about 380 cps and higher.
The (II, IV, and V) branched, star-shaped (radial), or multiarm block copolymers are characterized as having a Brookfield Viscosity value at 5 weight percent solids solution in toluene at 30xc2x0 C. of from about 80 cps to about 380 cps and higher, advantageously from about 150 cps to about 260 cps and higher, more advantageously from about 200 cps to about 580 cps and higher, and still more advantageously from about 100 cps to about 800 cps and higher.
The crystal gels can be made in combination with a selected amount of one or more selected polymers and copolymers (II) including thermoplastic crystalline polyurethane elastomers with hydrocarbon blocks, homopolymers, copolymers, block copolymers, polyethylene copolymers, polypropylene copolymers, and the like described below.
The crystal gels of the invention are also suitable in physically interlocking or forming with other selected materials to form composites combinations. The materials are selected from the group consisting of paper, foam, plastic, fabric, metal, metal foil, concrete, wood, glass, various natural and synthetic fibers, including glass fibers, ceramics, synthetic resin, and refractory materials.
The high tear resistant soft crystal gels are advantageously suitable for a safer impact deployable air bag cushions, the higher tear resistant crystal gels are advantageously more suitable, and the highest tear resistant crystal gels are advantageously even more suitable for such use and other uses.
The various aspects and advantages will become apparent to those skilled in the art upon consideration of the accompanying disclosure.
The crystal gels of the invention can be formed into gel strands, gel tapes, gel sheets, and other articles of manufacture in combination with or without other substrates or materials such as natural or synthetic fibers, multifibers, fabrics, films and the like. Moreover, because of their improved tear resistance and resistance to fatigue, the crystal gels exhibit versatility as balloons for medical uses, such as balloon for valvuloplasty of the mitral valve, gastrointestinal balloon dilator, esophageal balloon dilator, dilating balloon catheter use in coronary angiogram and the like. Since the crystal gels are more tear resistant, they are especially useful for making condoms, toy balloons, and surgical and examination gloves. As toy balloons, the crystal gels are safer because it will not rupture or explode when punctured as would latex balloons which often times cause injures or death to children by choking from pieces of latex rubber. The crystal gels are advantageously useful for making gloves, thin gloves for surgery and examination and thicker gloves for vibration damping which prevents damage to blood capillaries in the fingers and hand caused by handling strong shock and vibrating equipment. The crystal gels are also useful for forming orthotics and prosthetic articles such as for lower extremity prosthesis described below.
The EB copolymer midblock of conventional SEBS is almost totally amorphous and the EP midblock of SEPS is amorphous and non-crystalline.
Gels made from such block copolymers are rubbery and exhibit substantially no hysteresis. Their rubbery-ness and lack of hysteresis are due to the amorphous nature of their midblocks. Such gels are hereafter referred to as xe2x80x9cnon-crystalline gelsxe2x80x9d or more simply as xe2x80x9camorphous gelsxe2x80x9d.
In general, the overall physical properties of amorphous gels are better at higher gel rigidities. The amorphous gels, however, can fail catastrophically when cut or notched while under applied forces of high dynamic and static deformations, such as extreme compression, torsion, high tension, high elongation, and the like. Additionally, the development of cracks or crazes resulting from a large number of deformation cycles can induce catastrophic fatigue failure of amorphous gel composites, such as tears and rips between the surfaces of the amorphous gel and substrates or at the interfaces of interlocking material(s) and gel. Consequently, such amorphous gels are inadequate for the most demanding applications involving endurance at high stress and strain levels over an extended period of time.